Movable magnet loudspeaker

ABSTRACT

A transducer device such as a loudspeaker or microphone has the electrical coil stationary with respect to the acoustic diaphragm. The diaphragm is actuated by a movable permanent magnet which interacts with the field of the stationary electrical coil. The preferred permanent magnet is one having a high torque-to-weight ratio with respect to an external field. The cobalt-rare earth magnets are examples of such permanent magnets.

United States Patent Parker 1451 Mar. 19, 1974 1 MOVABLE MAGNET LOUDSPEAKER 2.492.255 12/1949 Angehm 179/119 R [75] Inventor: Rollin James Parker cream/me, 3.651.283 3/1972 Doschek 179/1l5.5 R

Mi h. FOREIGN PATENTS OR APPLICATIONS Assignee: General Electric p y New 1.037510 8/1958 Germany 179/114 York. NY. Przmary Exammer-Kathleen H. Claffy F 116d? J 1972 Assistant Examiner-Thomas L. Kundert 21] Appl. No.: 265,250

[ ABSTRACT 52 US. Cl. 179/114 R, 179/117 A transducer device Such as a 10(Speaker 51 1m. 01 11041 11/02 Phone has the electrical Stationary with respect 58 Field of Search 179/114 R, 114 A, 115 R, the acoustic diaphragm The diaphragm is e by 179/117 119 A, 1 15 A; 148/101, 31 R 3157 a movable permanent magnet which interacts with the field of the stationary electrical coil. The preferred [56] References Cited permanent magnet is one having a high torque-toweight ratio with respect to an external field. The 00- 2 H0 153 Z I I PATENTS 179/115 R halt-rare earth magnets are examples of such perma- O St et a t a t I 3,682,715 8/1972 Martin nen m gn 5 3076.062 1/1963 Fener .1 179/119 A 3 Claims, 6 Drawing Figures PATENTEDHAMS I974 3798.891

FIG-l 1151.

FIG.5 FIG-6 MOVABLE MAGNET LOUDSPEAKER BACKGROUND OF THE INVENTION Transducers such as loudspeakers and microphones used for converting electrical energy into linear mechanical motion and vice versa have conventionally had a relatively large stationary permanent magnet coupled to interact with a movable electrical coil which is connected to a membrane or diaphragm so arranged that when the coil is moved it imparts a corresponding movement to the membrane or diaphragm and when the membrane or diaphragm is moved it imparts a corresponding movement to the coil. When such a transducer is used as the actuating element in a loudspeaker of the type used in television and radio broadcast reception great care in manufacture is necessary in order to insure proper tolerances between the moving coil and permanent magnet structure. In addition, the mass of the moving coil is very critical because of acoustic tonal balance problems.

Thus, the conventional transducer not only has engineering requirements which must be satisfied but also requires considerable manual adjustment and care during the course of manufacture. It is a labor-intensive component to manufacture.

SUMMARY OF Tl-IE INVENTION This invention is directed broadly to an arrangement of parts in a transducer whereby a stationary electrical coil is coupled to interact with a movable permanent magnet to translate an electrical signal impressed on the coil into movement of the permanent magnet thereby converting the electrical signal into a mechanical motion. In a preferred form the permanent magnet has a high torque-to-weight ratio with respect to the field of the electrical coil. Cobalt-rare earth magnets are the preferred form of such permanent magnets.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic diagram of a transducer in accordance with this invention showing a transversely magnetized rectangular magnet element.

FIG. 2 is a schematic diagram of a transducer providing axial magnetization wherein the permanent magnet is in the form of a ring which provides 360 magnetization.

FIG. 3 is a simplified form of FIG. 2 in which the permanent magnet is comparable to a segment of the ring magnet of H6. 2 and is, in fact, a bar magnet. The suspension system comprises a resilient pad between the permanent magnet and a steel pole piece.

FIG. 4 is a schematic diagram of a transducer which provides 360 radial magnetization with a return path.

FIG. 5 is a schematic diagram of a transducer similar to that of FIG. 4 except that there is no return path.

FIG. 6 is a schematic diagram of a transducer in which a pair of coils exert push-pull axial magnetic force on a permanent magnet.

DESCRIPTION OF THE PREFERRED EMBODIMENT In utilizing a permanent magnet as the element for translating electrical energy into mechanical energy, and vice versa, as provided by this invention, it is important that the permanent magnet have as high a reaction torque per unit of weightwith respect to an external magnetic field as possible. Such a torque is the product of the intrinsic magnetization of the permanent magnet and the strength of the external field. In the case of cobalt-rare earth magnets a very short heavily self demagnetized volume still has nearly the full intrinsic level of magnetization. Consequently, a low mass permanent magnet element of the cobalt-rare earth type can exert a very large force or torque in an external field.

The cobalt-rare earth magnets which are the preferred permanent magnets for use in this invention are of the type described in Becker US Pat. No. 3,501,358; Cech US. Pat. No. 3,625,779; and Benz US Pat. Nos. 3,655,463 and 3,655,464 which are incorporated herein by reference.

The torque achievable in a cobalt-rare earth magnet per unit of mass is greater by a factor of approximately 10 than older permanent magnet materials such as alnico. Of the rare earths (elements 59-72)samarium alloyed with cobalt has been shown to provide the greatest coercive force up to the present time. However, mixtures of rare earths commonly available under the designation mischmetal can be alloyed with cobalt to produce satisfactory permanent magnets for use in the practice of this invention. For purposes of this invention yttrium and cerium are included with the rare earth elements.

FIGS. 1-6 of the drawing illustrate typical arrangements of parts of the transducers of this invention. In all figures a membrane or diaphragm 10, which is usually of circular configuration and which may be coneshaped, is physically connected to a permanent magnet 11 by means indicated by a line 12. Movement of the permanent magnet 11 will impart comparable movement to the diaphragm 10 and movement imparted to the diaphragm 10 will impart comparable movement to the permanent magnet 11. The permanent magnet 11 is positioned to interact with any external magnetic field which may be produced by an electromagnet assembly consisting of a core 13 and coil 14 (FIGS. 1-4). The polarity of the permanent magnets 11 is indicated by the letters N and S. In FIG. 3 the magnet 11 is a bar magnet attached to a resilient pad 15 which is, in turn, mounted on a pole piece 16.

In operating the transducer of this invention as, for example, a loudspeaker, an electrical signal is fed to the coil 14 to produce a corresponding magnetic field which interacts with the permanent magnet 1 1. This interaction with the permanent magnet 11 converts the electrical signal to a corresponding mechanical movement in the permanent magnet 11. This movement is then transmitted to the diaphragm 10 which emits sound corresponding to the electrical signal introduced to the coil 14.

When a transducer of this invention is used as a microphone the diaphragm 10 is caused to vibrate in tune with sound vibrations striking it. This sets up movement in the permanent magnet 11 which creates a corresponding magnetic field in the electromagnet assembly to create an electrical signal which leaves the transducer by way of the coil 14.

The present invention provides high interactions between the field of the permanent magnet 11 and the field of the electromagnetic assembly provided by the core 13 and coil 14. Thus, larger tolerances between the permanent magnet 11 and core 13 are possible than is the case with moving coil dynamic speakers. These tolerances improve the reliability of the transducer device with respect to time and considerably reduce the cost of manufacture of such devices. In addition, the coil 14, being stationary, is no longer limited as to weight. Consequently, it can be provided with a highimpedance winding and thereby eliminate the need for a coupling transformer. A speaker built according to the embodiment of FIG. 2 gave comparable sound power output to a similar size dynamic moving coil speaker.

While the invention has been described with reference to certain specific embodiments it is obvious that there can be variations which properly fall within the scope of the invention. Accordingly, the scope of the invention should be limited only as may be necessitated by the scope of the appended claims.

What I claim as new and desire to secure by letters patent of the United States is:

l. A device for converting an electrical signal into an acoustical sound output comprising a U-shaped core of magnetically permeable material, a stationary electrical coil around said core for the creation of an electromagnetic field, a pole piece mounted on each protruding end of said core, the pole pieces defining a gap between the protruding ends of said core, a resilient nonmetallic pad bridging said gap, and a movable permanent magnet positioned on said pad to interact with said electromagnetic field and move in response to the electrical field impressed upon said stationary electrical coil.

2. A device as claimed in claim 1 wherein the permanent magnet is a cobalt-rare earth magnet.

3. A device as claimed in claim 1 wherein the permanent magnet is a cobalt-samarium magnet. 

1. A device for converting an electrical signal into an acoustical sound output comprising a U-shaped core of magnetically permeable material, a stationary electrical coil around said core for the creation of an electromagnetic field, a pole piece mounted on each protruding end of said core, the pole pieces defining a gap between the protruding ends of said core, a resilient nonmetallic pad bridging said gap, and a movable permanent magnet positioned on said pad to interact with said electromagnetic field and move in response to the electrical field impressed upon said stationary electrical coil.
 2. A device as claimed in claim 1 wherein the permanent magnet is a cobalt-rare earth magnet.
 3. A device as claimed in claim 1 wherein the permanent magnet is a cobalt-samarium magnet. 